Java

The standout Java project is Crafting Interpreters by Robert Nystrom, a free online book. Chapters 4 to 13 build jlox, a complete tree-walking interpreter for a small scripting language in Java, covering scanning, parsing, resolving variables, closures and classes. It is long, but every chapter ends with working code, and the second half of the book rebuilds the same language as a bytecode VM in C.

The other tutorials are shorter. Build a Simple HTTP Server with Java uses ServerSocket to answer browser requests and shows what a web server does under the hood. Build a Spring Boot App with User Authentication is the official Spring guide to securing a web application with Spring Security and a login page. Build an Android Flashlight App is a short video project for a first Android app.

A good order is the HTTP server first, then the Spring Boot guide, then Crafting Interpreters once you are comfortable with classes, interfaces and recursion.